An aldose reductase is an enzyme which catalyzes the conversion of aldose in vivo, e.g. glucose or galactose into its corresponding polyol, e.g. sorbitol or galactitol, respectively. It is known that the sorbitol and galactitol produced by the action of this enzyme are accumulated in the lenses, the peripheral nerves, the kidney, etc., of diabetics and galactosemiacs, thus causing complications of diabetes, e.g. retinopathy, diabetic cataract, neuropathy and nephropathy. Thus the inhibition of the enzyme aldose reductase permits the prevention or treatment of the above-described complications.
Japanese Patent Application Kokai Nos. 57-28074, 60-156387 (EP-A 0 047 109) and 60-136575 (EP-A 0 143 461) disclose that rhodanine derivatives possess an inhibitory activity against aldose reductase. However the compounds disclosed therein are structurally different from those of the present invention in respect of the nitrogen atom on the rhodanine ring being substituted.
Japanese Patent Application Kokai No. 64-52765 discloses that the compounds wherein the nitrogen atom on the rhodanine ring is not substituted possess an inhibitory activity against aldose reductase. However those compounds are also structurally different from the compounds of the present invention with respect of the substituents attached to the 5-position through a double bond.